Snd is a sound editor modelled
loosely after Emacs. It
can be customized and extended
using either s7 (included in the Snd sources),
Ruby, or
Forth.
Snd is free; the code is available via anonymous ftp as
snd-17.tar.gz.
Snd has a home page
and a CVS repository, and
is included in PlanetCCRMA.

where "some.snd" is any available sound file. You should
get a window with the first .1 seconds of the sound displayed as a time
domain waveform. Click the file name at the lower left to get
some information about the file. Click the "f" button, and an fft window
appears alongside the waveform. Drag the upper scale at the
bottom of the graph and both graphs are updated as you move
through the file. Drag the lower scale to zoom in or out.
Drag the outer scale (the wider one) on the left to change
the y axis bounds. The inner scale
moves the y axis up and down.
Click the "w" button (unset it) and
the time domain waveform goes away. Click "play" to
play the file. "sync" is more complicated — it is used
to group sounds together for simultaneous editing.

Now return to the time domain form (click "w" and "f"),
and click in the graph itself. A red cursor (a big "+")
appears at that point. The cursor is just like an
Emacs cursor — you can delete the sample at the cursor,
for example, by typing control D (abbreviated in this
document C-d), or move back one pixel with C-b.

Click and drag the mouse through some portion of
the graph — the portion dragged is highlighted in
some way. When you release the mouse button, the
highlighted portion becomes a
'selection' that you can play, delete, or mix elsewhere.
If you place the mouse toward the top of the graph at the selection
boundary, the cursor changes to a double-arrow, and you can drag the
boundary. There's a triangular area beneath the x axis at the
start and end of the selection. Click the left one to play (or stop playing)
the selected portion; the right one starts a looping play. The cursor,
marks, and mixes also have associated play arrows (triangles).

You'll
notice if you make some change to the data that
the file name gets an asterisk, as in Emacs, and
the various 'undo' and 'redo' menu options come
to life. Just for laughs, delete the selection (via the Edit menu), then click the right mouse
button to get the popup menu, and try Undo followed
by Redo.

Next type C-m. This places a
mark at the current cursor location. C-a goes
to the start of the window; C-j jumps forward to the
next mark. Click and drag the upper horizontal
mark portion to move the mark; click the triangular
lower portion to play from the mark. If you are
editing a multichannel file, control-click the
triangle to play all channels together from the mark.

Finally, go to the View menu and select 'Show controls'.
A new portion of the Snd window opens, containing
a number of controls. Try goofing around with them
while playing the sound. For the more complex
cases, the button on the right side turns the
option on or off.

But this is all standard stuff; even the
various dialogs scattered around the menus will present
no surprises.
The GL spectrograph is somewhat unusual,
and I like the paned window approach to multichannel sounds ("de gustibus...").
But it is primarily the embedded extension language
(s7, Ruby, or Forth) that
makes Snd different from other editors.
Everything in Snd from the low-level data readers to the
high-level editing operations is tied into the extension
language. You can do anything you want with sounds.
Rather than try to present endless menus full of
canned effects, Snd gives
you full programming power over sounds, and you can
extend it to include whatever you want. But if you
are in a big hurry, or not yet confident in your ability as a programmer, many such
operations have been included in the various scm (s7 = Scheme),
rb (Ruby), and fs (Forth) files in the Snd tarball. Dave Phillips
wrote a set of files that implement dozens of the effects and
editing operations built into other editors. Just load the
files that look interesting, and start clicking widgets.

Manipulating sounds in a programming environment
is most enjoyable if you can edit and retry expressions
easily. Old-time Lispers called this special kind of
text widget a "listener". There is one in Snd — see
the View:Open Listener menu. The listener has a prompt (">")
at which you can type any expression: (+ 1 2)
which it then evaluates, returning the result.
I normally work in the listener, leave the menus
untouched, and use the mouse to scan
through the current sound data.

The rest of this document describes the user interface; extsnd.html
presents the programming interface; grfsnd.html describes Snd's connection
to various other programs and X; sndscm.html has brief descriptions of
most of the Scheme/Ruby/Forth code included in the Snd tarball; fm.html
is an introduction to FM; sndclm.html is the basic generator documentation;
sndlib.html describes the underlying sound IO library;
s7.html is the s7 documentation.

When invoked, Snd scans
its arguments for file names, and opens any it finds.

snd oboe.snd fyow.snd

If there are no arguments, Snd comes up as a bare menu bar.
If a name is preceded by "-p" or "-preload", it is treated as a directory
name, and all sound files found in that directory are added
to the View:Files list. To
load arbitrary Snd customizations (your own code, or a saved state file),
precede the file name with "-l" or "-load" (or use the load function).

Normally Snd adds each new sound below those currently being
displayed.
To position sounds horizontally (adding on the right), use the "-h" (or "-horizontal") flag.
Other overall layout
choices include the Notebook widget (-notebook),
and separate windows for each sound (-separate).

A file can be opened from the File menu via Open
or View. View opens the file read-only, whereas Open
allows it to be changed. The equivalent keyboard
command is C-x C-f.
If a file cannot be changed (either it was opened read-only
or you don't have write permission for it), a lock appears
next to the file name. Similarly, if Snd notices that
the file on the disk no longer matches the original,
a warning is posted. This can happen if some other program
writes a sound while you are editing an earlier version
of it.
If the variable auto-update is #t (the default is #f), Snd
automatically updates any such file.

The file selection dialog is slightly different from the Motif or Gtk default. If you single click
in the directory list, that directory is immediately opened and displayed. Also there are
a variety of context-sensitive popup menus to handle special chores such as setting the
current sort routine (right click over the file list), jump to any higher level directory (right click
in the directory list), choose a recently opened file (click in the filename text widget), or
return to a previous list of files (click in the filter text widget).
The 'sound files only' button filters out all non-sound files from the files list, using the
extension; you can add to the list of sound file extensions via add-sound-file-extension.
The built-in extensions are
"snd", "wav", "aiff", "aif", "au", "aifc", "voc", and "wve".
When a sound file is selected, information about it is posted under the lists, and a 'play'
button is displayed. The name field has TAB completion, of course, and also
watches as you type a new name, reflecting that partial name by moving the file list to
display possible matches.

The files can have any number of channels.
Data can be either big or little endian.
A 'New' file (one created by the File:New option) can get its type and so on from
the default output variables such as default-output-header-type,
or from a dialog that pops up when some field has not been set
in advance.
Similary, a raw data file gets its srate, chans,
and sample type information either from the open-raw-sound-hook
or from a dialog window that pops up when such a file
is opened. The file types listed above as "automatically translated" are
decoded upon being opened, translated to some format Snd can read and write,
and rewritten
as a new file with an added (possibly redundant) extension .snd,
and that file is the one the editor sees from then on.

Each file has its own
'pane', a horizontal section of the overall Snd
screen space; within that section, each channel
has a pane, and below the channels is the 'control
pane', normally hidden except for the file name
and 'status area'. At the very bottom
of the Snd window is the listener, if any (see
the View menu Open listener option).
The panes can all be independently
raised and lowered by dragging the pane buttons on
the right.
Each channel has the
four scrollbars setting what portion of the data
is displayed; the 'w' button (normally set) which
causes the time domain waveform to be displayed;
and the 'f' button (normally unset) which includes
the frequency domain (FFT) display.
There is a third display settable by user-provided
functions; if both the 'w' and 'f' buttons are
off and there is no active user-display function,
you get an empty display. For each sound there is
a control panel containing the file name, in parentheses if
the file is actually a link, with an
asterisk if there are unsaved edits, a 'status area'
for various kinds of simple text-based interactions,
a 'sync' button for grouped display and edit
operations, a 'unite' button (if the sound has more than one channel),
and a 'play' button to play the
current (edited) state of the file.

To close a file (flushing any unsaved edits), use
the File:Close option, or C-x k. This command
applies to the currently selected sound.

To save the current edited state of a file, use the
Save option (to overwrite the old version of the
file), or Save as (to write to a new file, leaving
the old file unchanged). The equivalent keyboard
command is C-x C-s (save).
Normally, if the new file already exists, and it is
not currently being edited in Snd, it is silently
overwritten. If you try to overwrite a file, and
that file has active edits in a different Snd window, you'll be asked
for confirmation.
If you want Snd to ask before overwriting
a file, set the variable ask-before-overwrite to #t.
If you edit a write-protected file and try to save the edits, Snd will
try to save the edits in a temporary file and will post a warning
that the current file can not be overwritten.
To extract just one channel of a multichannel file from the Save-as dialog,
put the desired channel number (0-based) in the "extract channel" field,
then click 'Extract'.

To undo all edits and return to the last saved state
of a file, use the Revert option. The edit history
is still available, so you can redo all the edits
in order by calling Redo repeatedly.
There's also a list on the left of each channel pane containing a list of
the current edits. You can click anywhere in the list to move to that
edit.

The Print option opens the Print
dialog. You can send the currently active graph directly to
a printer, or save it as an encapsulated Postscript
file. The default name
of this file is "snd.eps"; it can be set via eps-file.

Finally, to exit Snd cleanly (that is, removing any
temporary files, and cleaning up some system stuff),
use the Exit option. Unsaved edits are silently
flushed (but see the function ask-about-unsaved-edits).

The sound display can be modified in various ways. Choose View:Graph style:dots
to view the sound as dots rather than connected lines
(see also dot-size).

Similarly, to show (or hide) the line
Y = 0, use the y=0 option. The Region browser is described under
Regions. To open the control panel, use Show Controls.
To open or close the listener, use Open listener.

The Color/Orientation option
activates a window that sets various aspects of the sonogram, spectrogram,
and wavogram displays. There are fifteen or so colormaps available along with
ways to invert the maps, and scale (darken) them differently according to screen or
printer characteristics.

The Popup menu's Info dialog can be left in view and updated with M-v i
to reflect the currently active sound. The same information is displayed in the
status area when you click the file name.

In the Motif version of Snd, the View Files option
starts a dialog with a list of interesting files,
controls for amplitude, speed (sampling rate change), and amplitude envelope,
and buttons to mix, insert, or open the selected files.
This dialog is sort of a combination of the File:Mix and View:Mixes dialog, aimed
at making it easy to toss together bunches of sound files.
In the file list, the button on the left plays the file.
Single-click a file name to select it; double-click a file name to open it in Snd.
The 'update' button runs through the file
list checking for files that have been deleted or moved behind Snd's back.
'sort' is a drop-down menu of file sorting possibilities.
You can add to this list either by dragging file icons around the screen (which I think
is a very awkward thing to do), or by calling add-file-sorter and friends, or
by typing the file or directory name in the 'add:' text widget.

Files can be added to the list at startup
via the -p switch, and with the functions add-file-to-view-files-list
and add-directory-to-view-files-list.
The 'Mix' button mixes in the currently selected sound, and 'Insert' inserts it.
See nb.scm for an extension of this dialog that posts various kinds of information
about each file as the mouse passes over it.

Transform Options applies mainly to the FFT display triggered
by setting the 'f' button in the channel window. The dialog that is
launched by this menu item has six sections: on the upper left
is a list of available transform types; next on the right is a
list of fft sizes; next is a panel of buttons that sets various
display-oriented choices; the lower left panel sets the current
wavelet, when relevant; next is the fft data window choice; and
next to it is a graph of the current fft window with the spectrum of that window
in blue.
When the window
has an associated parameter (sometimes known as "alpha" or "beta"),
the slider beneath the window list is highlighted and can be used
to choose the desired member of that family of windows.

The FFT is taken from the start (the left edge) of the
current window and is updated as the window bounds change.
If you'd like the fft size to reflect the current time domain
window size:

The fft data is scaled to fit between 0.0 and 1.0 unless
transform normalization is off.
The full frequency axis is normally displayed, but the
axis is draggable — put the mouse on the axis and
drag it either way to change the range (this is equivalent
to changing the variable spectrum-end). You can also click
on any point in the fft to get the associated fft value at that point
displayed; if with-verbose-cursor is on, you can
drag the mouse through the fft display and the
description in the status area will be constantly
updated.

The transform is
normally the Fourier Transform, but others are available, including
about 20 wavelet choices, and autocorrelation.

The top three buttons in the transform dialog choose between a normal
fft, a sonogram, or a spectrogram. The peaks
button affects whether peak info is displayed alongside the graph
of the spectrum. The dB button selects between
a linear and logarithmic Y (magnitude) axis. The log freq
button makes a similar choice along the frequency axis.

The easiest way to change the colormap and graph orientation
of the spectrogram, wavogram, and sonogram, is to use the Color/Orientation
dialog from the View menu.
The keypad keys are mapped to various variables as follows:

The keypad Enter key resets all the
spectrogram variables to their default values.
The keypad arrow keys zoom and move the fft spectrum.

If your time domain data can be viewed as a series of slices
through a 3-D landscape, you can use the
"wavogram" to mimic the spectrogram in the time domain.
The first trace is at the bottom of the graph, moving from left to right.
The same rotation commands apply to this display,
with the additional variable wavo-hop which sets the
density of the traces. To get this display (set! (time-graph-type) graph-as-wavogram). It is
important to set the length of each trace
so that successive peaks line up. The
trace length in samples is set by the variable wavo-trace,
or the numeric keypad + and - keys.

The Zoom style option chooses which graph point to center on
during an x-axis zoom.
The default is to zoom onto the cursor or the beginning of the current
selection if either is visible. You can also have
zoom focus on the left edge, right edge, or
midpoint of the current window.

The Preferences dialog tries to make it easier to set up Snd initially. It is a GUI-based way to
write your initialization file. Most of the global variables are included, and a number of
ancillary functions that seem to be popular. It's not yet completed, but more than 100 topics
are currently included — a good start!
To get more help on a particular topic, scroll horizontally to the list of topic names on
the far right, and click on the one you're
interested in. If you leave the help dialog active, it becomes a sort of tooltip —
if you linger over some other topic, its help info will be posted in the help dialog.

Editing in Snd is modelled after Emacs in many regards. Each
channel has a cursor (a big "+"), a set of marks, and a list of
edits that have not yet been saved. Most operations take place
at the cursor. Operations can be applied simultaneously to
any other channels or sounds by using the 'sync' button.
Operations can be applied
either to a sample, a selected portion, a channel, a sound, or any number of
sounds at the same time. Where an operation has an obvious
analog in text editing, I've tried to use the associated Emacs command.
To delete the sample at the cursor, for example, use C-d.

The following sections describe how to move the cursor and
the window; how to change which channel is active;
how to use marks and regions; how to perform various
common editing operations. It ends with a description of
all the mouse and keyboard editing commands. The 'control
panel' provides more complex editing operations, but
has a chapter to itself.

The selected channel receives keyboard commands. You can
also move between windows with C-x o.

Moving the cursor

Any mouse click on the waveform causes the cursor to move to that point.
"The cursor" here refers to the sample cursor, normally a big "+". There is also the
cursor associated with the mouse which is a slanting arrow outside the graph, but
changes to a small "+" inside the graph. When the mouse
is hovering over something that can be dragged (a selection edge, a mark, a mix, etc),
it changes to a double arrow. When a mouse click will start sound playing,
it becomes a right arrow. And when it's over the selection
loop-play triangle, it's a left arrow. But the main cursor in Snd is the big "+" that marks a particular sample.
To move it from the keyboard, use:

All keyboard commands accept numerical arguments, as in Emacs.
If the argument is a float, it is multiplied by the sampling
rate before being applied to the command, so C-u 2.1 C-f moves
the cursor forward 2.1 seconds in the data.

Moving the window

The simplest way to move the window (the portion of the data in the current graph) is to drag the
scrollbars with the mouse. The darker scrollbars zoom in and
out; the lighter bars move the window along the x or y axis.
To move by a single window, click the
arrows on the scrollbar. To move by smaller amounts,
use the left and right arrow keys (or zoom with the up and
down arrow keys); the control, shift, and meta keys
are multipliers on this movement — each key adds a factor
of .5 to the multiple, so to move by .25 windows,
press control, meta, left (or right) arrow. A similar
mechanism can be used to zoom quickly onto a particular
point; hold the keys and click the mouse in the waveform
and you'll zoom an increasing amount into the data at that
point.

Various keyboard commands provide
much more precise control of the window bounds and placement:

C-l position window so cursor is in the middle
C-x b position window so cursor is on left margin
C-x f position window so cursor is on right margin
[Down] zoom out, amount depends on shift, control, and meta
[Up] zoom in
[Left] move window left
[Right] move window right
C-x l position selection in mid-view
C-x v position window over current selection
C-x C-b set x window bounds (preceded by number of leftmost sample)
C-x C-p set window size (preceded by size as numeric argument)

As in most other cases, the sample numbers (or sizes) can be floats;
if the argument is not an integer, it is multiplied by the sampling
rate before being applied to the command. So, C-u .1 C-x C-p makes
the window display .1 seconds of data.
If you'd like far more precise window moving and zooming control,
see move-one-pixel and
zoom-one-pixel.

Marks

A 'mark' marks a particular sample in a sound (not a
position in that sound).
If we mark a sample, then delete 100 samples before it,
the mark follows the sample, changing its current position
in the data. If we delete the sample, the mark is also
deleted; a subsequent undo that returns the sample also
returns its associated mark. I'm not sure this is the
right thing, but it's a lot less stupid than marking
a position.

Once set, a mark can be moved by dragging the
horizontal tab at the top. Control-click of the tab followed by mouse
drag will drag the underlying data too, either inserting zeros or deleting data.
Click on the triangle at the
bottom to play (or stop playing) from the mark.

A mark can be named or unnamed. It it has a name, it is displayed
above the horizontal tab at the top of the window. As with
sounds and mixes, marks can be grouped together through
the sync field; marks sharing the same sync value (other
than 0) will move together when one is moved, and so on.
See the marks chapter
for a further discussion of synced marks.
The following keyboard commands relate to marks:

C-m place (or remove if argument negative) mark at cursor
C-M place syncd marks at all currently syncd chan cursors
C-x / place named mark at cursor
C-x C-m add named mark
C-j go to mark

The distance from the cursor to a mark can be used as a numeric
argument for other commands by following C-u with C-m. Any
number in-between is the number of marks to jump forward before
getting the distance.

A region is a portion of the sound
data. Although I'm not completely consistent in this document,
the word "selection" is used to refer to the currently selected
(and highlighted) portion of the data; an operation such as
filter-selection affects the underlying data. A "region" on
the other hand, refers to the saved (copied) version of (the original form of) that
data that can be inserted or mixed elsewhere.
That is, when a portion is selected, it is (by default) saved as the new
region; subsequent edits
will not affect the region data.
You can disable the region creation by setting the variable
selection-creates-region
to #f (its default is #t which can slow down editing of very large sounds).
Regions can be defined by make-region, by dragging the mouse
through a portion of the data, or via
the Select All menu option.
If the mouse drags off
the end of the graph, the x axis moves, in a sense dragging
the data along to try to keep up with the mouse; the further
away the mouse is from the display, the faster the axis
moves. (One minor caveat: if you drag the mouse too quickly off the end
of the graph, making a grand sweeping gesture, the last portion
of the graph may be missed because the mouse updates are
coalesced by X; move deliberately as you near the end
of the sound). In large sounds, the mouse granularity can be
large, but you can zoom onto the start or end of the selected
portion and move them using selection-position
and selection-framples.
A region can also be defined with keyboard
commands, much as in Emacs. C-[space] starts the
region definition and the various cursor moving
commands continue the definition.

Once defined, the copied region
is added to a list of currently
available regions (the maximum list size is normally 16 — see max-regions).
The currently available regions can be view from the
View menu's Region browser:

'play' plays the region. The graphical
display
shows the waveform with arrows to move around in the
channels of multichannel regions. If you double click the region entry, it
loads the region into the main editor as a temporary
file. It can be edited or renamed, etc. If you save
the file, the region is updated to reflect any edits
you made.

If the current selection is active (displayed somewhere in the
current time domain displays), there are lots of functions that
can edit that portion of the current sounds.
If the 'selection' button is set in the transform options dialog,
(or equivalently, show-selection-transform
is #t), the fft display, if any, displays the transform of the selected portion.

The edit list

The current state of the undo/redo list can be viewed
as a scrolled list of strings in the pane on the left of the
graph.
If there are no
current edits, it just lists the associated file name
(i.e. the zero-edits state). As you edit the sound,
the operations appear in the edit list window. Click
on a member of the list to move to that point in the
edit list (equivalent to some number of undo's or
redo's).

The function save-edit-history saves the current
edit list as a loadable program (assuming the base sounds haven't changed in the
meantime). The file can be edited (it's just a text file with comments).
See Edit Lists for more details.

The Print command produces a PostScript
file which can be sent to directly a printer or saved for later use.

Delete, insert, mix

The fastest way to delete a section is to drag the mouse through it and
call the Edit menu's Delete selection option.
The current selection
can be pasted in
by clicking the middle mouse button. The
associated keyboard commands are:

The File:Insert menu option inserts a sound file at the cursor, and
the Edit:Insert Selection menu option does the same with the current selection.

Multichannel operations

Normally each operation applies only to the currently
active channel. If, however, the sound's 'sync' button is set,
the operations apply to every sound or channel that also
has the sync field set to the same value. If you click
the 'sync' button, its value is 1 and its color is blue;
C-click gives 2 and green, C-M-click gives 3 and yellow;
C-M-Shift-click gives 4 and red; any other value (set via
the syncing function) shows as a black button. The point
of all this is that only those sounds that share the sync value
of the current sound are considered to be sync'd to it; for example,
to make a stereo selection in one file, then paste it into some
other stereo file, set the sync buttons in each sound, but use
different values; that way, the channels within each sound are
sync'd together (giving stereo operations), but the sounds themselves
are separate.

A multichannel sound also
has a 'unite' button to the left of the 'sync' button.
If this button is set, all channels are displayed in
one graph; the x and y-axis scrollbars apply to all the
channels at once, as do the 'f' and 'w' buttons;
two new scrollbars appear on the right of the window;
the furthest right
scrollbar affects the placement of the window within
the overall set of graphs, and the scrollbar on its left
zooms in and out of the overall graph. For stereo files,
this is user-interface overkill, but the hope is to
accommodate sounds with many channels.
The View menu Channel style
option has the same effect but applies to all active
multichannel sounds. Control-click the unite button
to get superimposed channels.
If the channels are not combined (the default), control-click the 'f' or 'w' button in one
channel to affect all channels at once.

The superimposed channels display is not very useful if you're trying to
edit the sound; it's aimed more at FFT comparisons and so on.

To get multichannel selections, set the sync
button, then define the selection (by dragging
the mouse) in one channel, and the parallel
portions of the other channels will also be
selected.

Amplitude envelopes and scaling

An envelope in Snd is a list of x y break-point pairs.
The x axis range is arbitrary.
To define a triangle curve: '(0 0 1 1 2 0).
There is no preset limit on the number of
breakpoints. Envelopes can be defined with
define and referred to thereafter by name.
Use the envelope editor
to draw envelopes with the mouse.

To scale a file or selection by or to some
amplitude, use the functions:

scale-by scales the current sync'd channels by its arguments,
and scale-to scales them to its arguments (a normalization).
The arguments in each case are either a list of floats
corresponding to each successive member of the current
set of sync'd channels, or just one argument. In the
latter case, scale-by uses that scaler for all its
channels, and scale-to normalizes all the channels
together so that the loudest reaches that amplitude
(that is, (scale-to .5) when applied to a stereo file
means that both channels are scaled by the same amount so
that the loudest point in the file becomes .5). There's
one special case here: if you (scale-to 1.0) in a sound
that is stored as short ints and you haven't set the clipping
variable to #t, since 1.0 itself is not representable,
the actual scaled-to value is just less than 1.0 to avoid the
(unwanted) wrap-around.

Find

Searches in Snd refer to the sound data, and are,
in general, patterned after Emacs. When you type
C-s, the find dialog is activated.
The expression it asks for is a
function that takes one argument, the current
sample value, and returns #t when it finds a match.
To look for the next sample that is greater than
.1, (lambda (y) (> y .1)). The
cursor then moves
to the next such sample, if any.
Successive C-s's
repeat the search.
These searching functions can be closures; the following searches for
the next positive-going zero crossing, placing the cursor just before it:

Now C-s (zero+) followed by C-s's moves to successive zero crossings.
There are more examples in sndscm.html.

Change samples

The simplest changes are:

C-z set current sample to zero
C-x C-z smooth data using cosine (smooth-sound)

(set! (sample (cursor)) .1) sets the sample
at the cursor to .1. To set several samples to zero, use C-u <number> C-z.

Undo, redo, revert

Snd supports 'unlimited undo' in the sense that you can
move back and forth in the list of edits without any
limit on how long that list can get. The data displayed is
always the edited form thereof. Each editing operation
extends the current edit list; each undo backs up in that
list, and each redo moves forward in the list of previously
un-done edits. Besides the Edit and Popup menu options, there
are these keyboard commands:

To play a sound, click the 'play' button. If the sound has more
channels than your DAC(s), Snd will (normally) try to mix the extra channels
into the available DAC outputs.
While it is playing,
you can click the button again to stop it, or click some other
file's 'play' button to mix it into the current set of sounds
being played. To play from a particular point, set a mark
there, then click its 'play triangle' (the triangular portion
below the x axis). (Use control-click here to play all channels
from the mark point).
To play simultaneously from an arbitrary
group of start points (possibly spread among many sounds),
set syncd marks at the start points, then click the play
triangle of one of them.
The Edit menu 'Play' option plays the current
selection, if any.
And the region and file browsers provide
play buttons for each of the listed regions or files. If you
hold down the control key when you click 'play', the cursor
follows along as the sound is played. If 'verbose cursor' is
on, the time is also displayed in the status area.
If you stop the play
in progress, the cursor remains where you stopped it, but
otherwise returns to its original position. Type space
(without control) to pause and continue during playback.
The color of the play button corresponds to the state of
the playback: normal: not playing, blue: playing,
green: playing and tracking with the cursor (if any),
red: playback paused.

If you're getting
interruptions while playing a sound (stereo 44.1 kHz sounds can be problematic),
try using a very large dac buffer. Use set! to change this:
(set! (dac-size) 65536).
If you're getting clicks in Linux despite a large dac-size, try setting the OSS fragment sizes by hand:
(mus-oss-set-buffers fragments fragment-size). OSS's
defaults are 16 and 12 which make the control panel controls very sluggish. Snd used to
default to 4 and 12, but this seems to cause trouble for a variety of new sound cards.
My initialization file uses (mus-oss-set-buffers 2 12).

The keyboard commands for playing are:

C-q or space play current channel starting at the cursor
C-t stop playing
C-x p play region (numeric arg selects region)

In a multichannel file, C-q plays all channels from the current channel's
cursor if the sync button is on, and otherwise plays only the current channel.
While playing, space pauses playback or resumes it.
Except in the browsers, what is actually
played depends on the control panel.
Both C-q and C-x p allow overlapped plays; that is, if you
type C-q several times in succession, you'll hear several
simultaneous renditions of the sound. The various 'play'
buttons scattered around Snd on the other hand, interrupt
the current play if you click them during a run. C-g stops
any current playing. If no numeric argument is supplied,
C-x p plays the currently active selection.

Mix Files

Mixing (adding, not multiplying by a sinusoid) is the most common
editing operation performed on sounds, so there is relatively
elaborate support for it in Snd. To mix in a file, use the File Mix menu option,
the command C-x C-q, drag-and-drop it into its new home, or use one of the many mixing functions. Currently the only difference
between the first two is that the Mix menu option tries
to take the current sync state into account, whereas
the C-x C-q command does not. To mix a selection, use
C-x q.
In drag-and-drop, the mix starts at the mouse location;
in the other cases, the default is usually to
start at the current cursor location.
The mixed-in sound is displayed as a separate waveform above the main waveform with
a tag at the beginning. You can drag the tag to reposition the
mix. The amplitude, amplitude envelope, and speed (resampling rate) of the mixed-in portion can
be changed independently of anything else either through such functions as
mix-amp, or through the View:Mix Dialog.

The function make-sound-box
produces a container with each sound represented by an icon;
you can drag-and-drop the icon to the place where you want it mixed,
or drop it on the main menubar to open it.

The Mix dialog

The Mix Dialog (click a mix tag, or click Mixes in the View Menu) provides various
commonly-used controls on the currently chosen mix.

At the top are
the mix id (an integer), its begin and end times, and a play button for the mix.
Beneath that are various sliders
controlling the speed (resampling rate) and amplitude of the mix,
and beneath that an envelope editor for the mix's amplitude envelope.
The current mix amp env is not actually changed until you click 'Apply Env'.
The editor envelope is drawn in black with dots whereas the current
mix amp env (if any) is drawn in blue.
If the mix's sync field is not 0, any other mixes that share that sync field
are edited in parallel with the current one.

Change file format

To change the sound file's header or sample type, use the File or Edit menu Save as option.
Choose the header type you want, then the sample type,
(the sample type list will change depending on the header
choice). The File:Save dialog saves the currently selected sound.
The Edit:Save dialog saves the selection in a new file.

Extend a File

The easiest way to extend the
file is to pad it with zeros. Go to the end of the file,
via the C-> command, then use the C-u command with a float
argument, giving the number of seconds to add to the end
of the file, followed by C-o (insert zeros):
to add a second, C-> C-u 1.0 C-o. The same sequence
can be used to add silence to the start of a file.
Functions such as insert-sound
automatically pad with zeros, if necessary.

Edit or View an Envelope

The Edit Envelope dialog (under the Edit menu) opens a window
for viewing and editing envelopes.
The dialog
has a display showing either the envelope currently being edited or
a panorama of all currently loaded envelopes. The current
envelope can be edited with the mouse: click at some spot in the graph to place a
new breakpoint, drag an existing breakpoint to change
its position, and click an existing breakpoint to delete it.
The Undo and Redo buttons can be used to move around
in the list of envelope edits;
the current state
of the envelope can be defined in the extension language (and added to the envelope list on the left) with the 'define it' button.
Envelopes can also be
loaded from a separate file of envelope
definitions via load:

This defines two envelopes that can be used in Snd wherever an
envelope is needed. You can also define
a new envelope in the dialog's text field; for example,
'(0 0 1 1) followed by return creates a ramp.

In the overall view of envelopes,
click one, or click its name in the scrolled
list on the left to select it; click the selected envelope
to load it into the editor portion, clearing out whatever
was previously there. To load an existing envelope into the editor, you can
also type its name in the text field; to give a name to
the envelope as it is currently defined in the
graph viewer, type its name in this field, then
either hit return or the 'define it' button.

Once you have an envelope in the
editor, you can apply it to the current sounds
with the 'Apply' or 'Undo&Apply' buttons; the latter
first tries to undo the previous edit, then applies
the envelope.
The envelope can be applied to
the amplitude, the spectrum, or the sampling rate. The
choice is made via the three buttons marked 'amp',
'flt', and 'src'.
The filter order is the variable enved-filter-order
which defaults to 40. To use fft-filtering (convolution)
instead, click the "fir" button, changing its label to "fft".
If you are displaying the fft graph of the current channel,
and the fft is large enough to include the entire sound,
and the 'wave' button is set,
the spectrum is also displayed in the envelope
editor, making it easier to perform accurate (fussy?) filtering
operations.

To apply the envelope to the current
selection, rather than the current sound, set the 'selection' button.
To apply it to the currently selected mix, set the 'mix' button.
Control-click 'mix' to load the current mix amplitude
envelope into the editor.

The
two toggle buttons at the lower right choose whether
to show a light-colored version of
the currently active sound (the 'wave' button), and whether
to clip mouse movement at the current y axis bounds (the
'clip' button). The 'linear' and 'exp' buttons choose
the type of connecting lines, and the 'exp base' slider at
the bottom sets the 'base' of the exponential curves, just as
in CLM. If the envelope is being treated as a spectrum ('flt'
is selected), the 'wave' button shows the actual frequency
response of the filter that will be applied to the waveform
by the 'apply' buttons. Increase the enved-filter-order to
improve the fit. In this case, the X axis goes from 0 Hz to half the sampling rate, labelled as "1.0".

Edit, add, or remove the header

The Edit menu's Edit Header option starts a dialog to edit, add, or
remove the sound's header. No change is made to the actual sound
data; the new header is blindly written out; any unsaved edits are
ignored. If you specify 'raw' as the type, any existing header is
removed. This dialog is aimed at adding or removing an entire header,
or editing the header comments; anything else is obviously dangerous.
If you don't change the data location, it will be updated to
reflect any header changes; that is, unless you intervene, the
resultant header will be syntactically correct.
After writing the new header, you should either close or update the
associated sound.

Save session

At any time you can save the current
state of Snd by calling (save-state name) where name
is a file name. You can restart the saved session by calling Snd
with this file name and the "-l" switch: snd -l name.
This file is in exactly the same format as the initialization file, and can be edited, renamed, or
whatever. To load such a file after startup, (load name).

Center a tiny signal with DC

Due to the quantized nature of the y-axis position scroller, a tiny
signal that is not centered on 0 can be a pain to position in the
window. Use the y-bounds function to set the y axis bounds to some
small number, then use the position scroller to find the signal.
For example, if your signal is a very soft recording setting only the lowest two bits
of a 16 bit signal but with DC offset due to the recording conditions,
(set! (y-bounds) '(-.01 .01))
and try the scroller.

Miscellaneous commands

C-g at any point aborts the current keyboard command
sequence, as does any mouse click. C-g can also interrupt most long
computations (search, eval expression, and the various envelope applications).
If you notice one that is not interruptible, send me a note — I probably just
forgot about it.

C-u introduces a numeric argument. Besides the integer and
float cases mentioned several times above, you can also
use marks to set the argument. If the (optional) number
after C-u is followed by C-m, the resultant number passed
to the command is the distance (in samples) from the cursor
to the n-th successive mark. That is C-u C-m C-f is the
same as C-j.

C-x introduces an 'extended command'. It can be preceded
by a numeric argument or aborted with C-g. C-x halts any
on-going region definition.

As in Emacs or Tcsh, the Tab key in a text field invokes a context-sensitive completion function
that tries to figure out what the rest of the text probably should be. If it finds no matches,
the text flashes red; if it finds multiple matches and can't extend the current text, it flashes green.
In the listener, the choices are displayed in a scrolled list; the up and down arrow keys can move
the selection, carriage-return accepts the current selection, mouse click on any item accepts it, and
any other character removes the list.

The control panel

The control panel is the portion of each sound's pane
beneath the channel graphs.

The controls are: amp, speed, expand, contrast,
reverb, and filter.

'Speed' here refers to the rate at which the
sound data is consumed during playback.
Another term might be 'srate'.
The arrow button on the right determines
the direction Snd moves through the data.
The scroll bar position is normally interpreted
as a float between .05 and 20.

'Expand' refers to granular
synthesis used to change the tempo of events
in the sound without changing pitch. Successive
short slices of the file are overlapped with
the difference in size between the input and
output hops (between successive slices) giving
the change in tempo. This doesn't work in all
files — it sometimes sounds like execrable reverb
or is too buzzy — but it certainly is more
robust than the phase vocoder approach to the
same problem. The best quality time expansion
comes from rubber-sound in rubber.scm, but unfortunately
it only works on well-behaved sounds.
The expander is on only if the expand
button is set.

The reverberator is a version of Michael
McNabb's Nrev. In addition to the controls
in the control pane, you can set the reverb
feedback gain and the coefficient of the lowpass
filter in the allpass bank (see below).
The reverb is on only
if the reverb button is set. The reverb length
field takes effect only when the reverb is
set up (when the DAC is started by clicking
'play' when nothing else is being played).

'Contrast enhancement' is my name for a
somewhat weird waveshaper or compander. It
phase-modulates a sound, which can in some
cases make it sound sharper or brighter.
For softer sounds, it causes only an amplitude
change. To scale a soft sound up before
being 'contrasted', use the variable
contrast-control-amp. The function maxamp
returns the channel's maximum amplitude, so the
inverse of that is a good first guess for
contrast-control-amp. Contrast is on only if the contrast
button is set.

The filter is an arbitrary (even) order FIR filter
specified by giving the frequency response
envelope
and filter order in the text windows provided.
The envelope X axis goes from 0 to half the sampling rate — see filter-control-in-hz.
If you raise the control pane from its default height,
a graph is revealed beneath the filter text field;
this is an envelope editor like the envelope editor dialog
but specialized for filtering. The actual frequency response (given the current filter order)
is displayed in blue. As with all the user interface text entry widgets,
anything you type in the filter envelope text field is evaluated,
returning in this case a list of breakpoints; you can
define a function that returns the list you want, then call that function
in the text field.
The filter is on only if the filter button is set.

There are many variables that reflect or control
the panel's various sliders; each also has a default
value. The reverb and expand functions also have
several aspects that aren't brought out to sliders or
buttons on the panel, but that can be accessed through
these variables. See the control panel section for details.

To take the current panel settings
and turn them into an edit of the
sound, call apply-controls. This may change
the length of the file; for example, if reverb is
on, the reverb decay length is added onto
the end. Once apply-controls has taken effect, the
controls section is reset to its clean state (so
a subsequent 'play' plays the unmodified newly
edited version).